1. Field of the Invention
The invention relates to an X-ray apparatus, comprising a polychromatic X-ray source for generating a primary beam of small cross-section, an energy-sensitive detector arrangement for detecting the scattered radiation generated by elastic scattering processes in the primary beam path, which detector arrangement comprises a plurality of detector elements which are arranged on rings concentric with the primary beam, and a collimator arrangement which is arranged between the X-ray source and the detector arrangement and which encloses the primary beam.
2. Description of the Prior Art
Of interest is commonly owned copending application Ser. No. 717,737 entitled "Arrangement for Measuring the Pulse Transmission Spectrum of X-ray Quanta" filed Jun. 19, 1991 in the name of G. Harding.
An X-ray apparatus of this kind is known essentially from DE-OS 37 12 928. Therein, the collimator arrangement is constructed so that the detector elements detect different sections of the primary beam within an examination zone and that a layer image of the scatter density can be formed when the examination zone is irradiated by the primary beam in different directions and along parallel beam paths.
It is to be noted that from GB-PS 1 463 054 an X-ray apparatus is already known which comprises an X-ray source for generating a primary beam of small cross-section and a detector arrangement for detecting the scattered radiation in the primary beam by means of a plurality of detector elements.
From the magazine "Phys. Med. Biol. " (1990, Vol. 35, No., 1, pp. 33-41) there is known an X-ray apparatus whereby the pulse transfer spectrum of a small area within a human body can be determined. Because the pulse transfer spectra of healthy and diseased (affected by osteoporosis) bones are clearly distinct, a method of this kind enables evaluation of the condition of the bone issue. For the detection of the pulse transfer spectrum, the radiation scattered at a fixed scattering angle (for example, 3.5.degree.) in the primary beam is detected by means of an energy-sensitive detector and the pulse transfer is determined in accordance with the equation EQU X=sin (T/2)/L (1)
where T is the scatter angle and L is the wavelength of the scattered radiation. Because for elastically scattered radiation the scatter cross-sections are comparatively small, the known apparatus has a comparatively low sensitivity, so that comparatively high radiation doses are required for such examinations. The radiation dose can be reduced by increasing the fixed, predetermined angular range within which the scattered radiation is detected, but the accuracy of determination of the pulse transfer is then reduced.